Narrow grip bench the same as standard

The weight I can BP with a narrow grip and standard grip is the same. For example, with a NG I can bench 300 lbs. for a single and sets of 5 with 270 lbs. With a standard grip- the same but no more. This despite training with a standard grip exclusively until the past month or so. It’s not really a problem but I’m just curious as to why I seem to gain no advantage with a grip that would seem mechanically superior, i.e. the standard grip.

How wide is your standard grip?

About a quarter inch inside the rings.

About a quarter inch inside the rings.